Depolymerization of lignin can yield phenolic monomeric platform molecules, but depolymerization and repolymerization are proposed as concurrent processes, which greatly limit the yield of monomeric products. Molecular-level characterization of heavy intermediates during depolymerization process is crucial for developing efficient methods to depolymerize raw lignin into monomers. In this study, a reactor-integrated negative-ion electrospray ionization high-resolution mass spectrometry was used to real-time analyze the lignin depolymerization process under operando conditions. Elemental composition, structural information as well as time-resolved evolution of a series of dimers and oligomers were obtained, which is hard to achieve with traditional GC-MS methods. The real-time evolution profiles of monomers, dimers, and oligomers reveals a possible repolymerization process during lignin depolymerization. These results provide insight into the complex lignin depolymerization process.
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